Epinephrine has a long history of pharmaceutical use that spans many decades since this catecholamine was first chemically synthesized at the turn of the twentieth century. Epinephrine is a sympathomimetic drug that acts on both alpha and beta adrenergic receptors found ubiquitously throughout much of the body. Epinephrine has profound effects on the cardiovascular system. Epinephrine has direct myocardial stimulation that increases the strength of ventricular contraction and cardiac output, positive inotropic action; increases heart rate, positive chronotropic action; and causes vasoconstriction in the veins and many vascular beds, positive vasopressor action. Epinephrine remains the first-line inotrope/vasopressor in many parts of the world and is recognized by the World Health Organization as an essential medicine with many medical uses and forms of administration.
As eye drops, epinephrine provides mydriasis, the dilation of the pupil, during intraocular surgery. As a solution for nebulization, epinephrine provides bronchodilation and relief of bronchospasm to asthmatics and those with chronic obstructive pulmonary disease. As a solution combined with analgesics for injection, including lidocaine for dental applications and bupivacaine for epidural analgesia, epinephrine improves and lengthens pain relief and sensory blockade during surgical procedures. Yet, epinephrine has many life saving uses in emergency room settings. As a solution for intramuscular or subcutaneous injection, epinephrine helps alleviate vasodilation, loss of intravascular fluid volume, hypotension, bronchospasm, and other symptoms associated with anaphylaxis, severe allergic reactions. Injections of epinephrine can also help stop bleeding, such as bleeding associated with peptic ulcers and surgical procedures. As a solution for intravenous injection, epinephrine is used as a critical adjunct in the treatment of cardiac arrest, e.g., to provide return of spontaneous circulation. Lastly, intravenous injection of this vasopressor provides critical care relief of hypotension associated with certain types of shock and fluid refractory shock, including septic shock.
Although epinephrine has many uses, including many life saving uses, existing liquid formulations of epinephrine are associated with reduced potency, less desirable effects, or have the potential to cause harm. Formulations of epinephrine are plagued by two major problems, racemization and oxidation. Racemization is the enantiomeric conversion of l-epinephrine into its less biologically active dextrorotatory isoform, d-epinephrine, which has a significantly low pressor effect; about one-fifteenth that of l-epinephrine. The d-isoform may also affect adrenergic receptor subtypes differently than the l-isoform, resulting in substandard and undesirable effects. Because the United States Pharmacopeia, USP, monograph for epinephrine injection does not include specifications for d-epinephrine content, only total epinephrine content, manufacturers of epinephrine drug products are not required to test the chirality of their formulation and significant racemization occurs, thus leading to a less potent product with less desirable effects. In actuality, the d-epinephrine isoform should be classified as an impurity in an l-epinephrine drug product. It is believed that the epinephrine injection USP monograph does not include specifications for d-epinephrine because preventing its formation through racemization had proven too challenging. Whereas, oxidation of epinephrine can be prevented to a certain extent, including the use of antioxidants. The oxidation of epinephrine's alcohol group forms its less potent ketone form, known as adrenalone, which has little if any beta adrenergic activity. Racemization and oxidation of epinephrine are associated with reduced potency and less desirable effects as the impurities d-epinephrine and adrenalone form at the expense of l-epinephrine.
Drug manufacturers try to deal with the problem of oxidation by adding bisulfite antioxidants and increasing overages, both of which have the potential to cause harm to patients. Preservatives, such as sodium metabisulfite, are added to epinephrine formulations as antioxidants to reduce oxidation and to help keep formulations sterile. Sterilization techniques themselves often result in the loss of total epinephrine, and l-epinephrine, which may be compensated with increased overages. Sodium bisulfite and sodium metabisulfite, bisulfites, can cause mild to severe, life-threatening allergic reactions, including anaphylaxis or asthmatic episodes in susceptible individuals, especially those with sulfite sensitivities. So while epinephrine is indicated for treating anaphylaxis, the presence of sulfites in its formulation puts susceptible patients at great risk of exacerbating their anaphylaxis to the point of death. And for patients who are in other critical situations, such as cardiac arrest or septic shock, such sulfite reactions could greatly worsen the critical condition of these vulnerable patients. Most formulations also use overages of active pharmaceutical ingredient to compensate for degradation of epinephrine content and activity over the course of the product's shelf-life. This results in epinephrine drug products released after manufacturing with a higher than expected activity, which could be hazardous to patients as causing higher infusion and injection doses, thereby increasing side effects such as tachycardia.
In addition to the degradants d-epinephrine and adrenalone, which have been mentioned to have little pharmacological activity compared with l-epinephrine, lesser other degradants include adrenochrome and adrenolotin. A potentially toxic impurity, epinephrine sulfonate, forms by sulfonation reaction in epinephrine drug products containing sulfites.
Due to the deficiencies in existing pharmaceutical formulations of l-epinephrine, the identity, strength, quality, purity, and/or potency of the drug product cannot be adequately assured, or neither can its safety. There exists a great need for a liquid formulation of 1-epinephrine that is both preservative-free and sulfite-free, with minimal overage, if any, and with minimal levels of degradants, including d-epinephrine, while maintaining a sterility guarantee. The present invention fulfills this great medical need by teaching improved l-epinephrine formulations, providing new methods of their preparation, and providing methods of safer medicinal use to achieve an improved standard of patient care.